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Abstract:

This printed circuit board (12) comprising: a first portion (20) having
first electronic components (22) of which the earth electrode is on a
first voltage source (14); a second portion (24) having second electronic
components (26) of which the earth electrode is on a second voltage
source (16); a third portion (28) inserted between the first portion (20)
and the second portion (24); a switched-mode power supply circuit (32)
connecting the first portion (20) and the second portion (24);
the said second portion (24) also comprising an electronic component (30)
powered by the said first voltage source (14),
is characterized in that it also comprises detection means (34) for
detecting a drop in electrical consumption of the component (30) and
switching means for switching the switched-mode power supply circuit (32)
when a predetermined drop in electrical consumption of the said component
(30) is detected.

Claims:

1. A printed circuit board comprising: a first portion having first
electronic components of which the earth electrode is on a first voltage
source; a second portion having second electronic components of which the
earth electrode is on a second voltage source; a third portion inserted
between the first portion and the second portion and forming a potential
barrier; a switched-mode power supply circuit connecting the first
portion and the second portion; the second portion also comprising at
least one electronic component powered by the said first voltage source
via the switched-mode power supply circuit; detection means for detecting
a drop in electrical consumption of the component; and switching means
for switching the switched-mode power supply circuit when a predetermined
drop in electrical consumption of the said component is detected.

2. The board according to claim 1, in which the switched-mode power
supply circuit comprises a transformer having a primary and at least one
secondary, the primary being connected to the first portion and the
secondary being connected to the second portion.

3. The board according to claim 2, in which the detection means is
further configured to detect a drop of an electrical current flowing in
the primary of the transformer below a predetermined current threshold as
a function of the predetermined drop in electrical consumption of the
component.

4. The board according to claim 3, in which the detection means comprises
a comparator.

5. The board according to claim 1, in which the electronic component is a
microprocessor controlling the power supply of a device via at least one
component amongst the second electronic components.

6. The board according to claim 5, in which the device is a motor of a
compressor.

7. The board according to claim 1, in which the predetermined drop
corresponds to an idling of the component.

8. The board according to claim 1, further comprising means for
inhibiting the switching means when the board is switched on.

9. A method for controlling a printed circuit board, the board
comprising: a first portion having first electronic components of which
the earth electrode is on a first voltage source; a second portion having
second electronic components of which the earth electrode is on a second
voltage source; a third portion inserted between the first portion and
the second portion and forming a potential barrier; a switched-mode power
supply circuit connecting the first portion and the second portion; the
second portion also comprising at least one electronic component powered
by the first voltage source via the switched-mode power supply circuit,
the method comprising the steps of: detection of a drop in electrical
consumption of the component; and switching of the power supply when a
predetermined drop in electrical consumption of the said component is
detected.

10. The method according to claim 9, in which the predetermined drop
corresponds to an idling of the component, and wherein the method further
comprises, before the switching step: reception by the component of an
instruction to switch the power supply; and idling of the component.

11. A compressor housing comprising a printed circuit board according to
claim 1.

Description:

[0001] The present invention relates to a printed circuit board, notably
for a compressor housing.

[0002] The invention relates more particularly to the field of compressors
driven electrically, used notably in the air conditioning systems of
motor vehicles.

[0003] Such a compressor is controlled with the aid of a microprocessor
incorporated into a printed circuit board placed on a housing of the
compressor.

[0004] This printed circuit board usually comprises three portions:
[0005] a first portion having first electronic components of which the
earth electrode is on a first voltage source; [0006] a second portion
having second electronic components of which the earth electrode is on a
second voltage source; and [0007] a third portion inserted between the
first and second portions and forming a potential barrier.

[0008] On this board, the microprocessor is incorporated into the second
portion while being powered by the first voltage source via a
switched-mode power supply circuit connecting the first portion and the
second portion.

[0009] In order to save electrical power, when the compressor is stopped,
it is necessary to switch the switched-mode power supply circuit.

[0010] The instruction to switch the switched-mode power supply circuit is
given by the microprocessor by sending a signal through the potential
barrier by means of an isolation component. Usually, the isolation
component used is an optocoupler.

[0011] However, the use of an optocoupler has several drawbacks.

[0012] Specifically, the use of an optocoupler in a motor vehicle
application is not easy because of problems of reliability of this
component which is not qualified for the motor vehicle sector. Moreover,
the addition of components involves additional volume and weight.

[0013] Furthermore, optocouplers are costly and have a limited service
life.

[0014] The invention proposes to improve the situation.

[0015] The object of the present invention is therefore to avoid the use
of an isolation component.

[0016] The invention first of all involves a printed circuit board
comprising: [0017] a first portion having first electronic components
of which the earth electrode is on a first voltage source; [0018] a
second portion having second electronic components of which the earth
electrode is on a second voltage source; [0019] a third portion inserted
between the first portion and the second portion and forming a potential
barrier; [0020] a switched-mode power supply circuit connecting the first
portion and the second portion;

[0021] the said second portion also comprising at least one electronic
component powered by the said first voltage source via the switched-mode
power supply circuit,

[0022] characterized in that it also comprises detection means for
detecting a drop in electrical consumption of the component and switching
means for switching the switched-mode power supply circuit when a
predetermined drop in electrical consumption of the said component is
detected.

[0023] For example, the first voltage source delivers a lower voltage than
that of the second voltage. In a particular example, the first voltage
source is a low voltage and the second voltage source is a high voltage.
Notably, in the context of the present application, a low voltage means a
voltage below 60 V and a high voltage means a voltage above 60 V.

[0024] Therefore, the present invention makes it possible to transfer the
instruction to switch the switched-mode power supply circuit from the
second portion to the first portion without passing through an isolation
component, by using detection of the drop in electrical consumption.

[0025] Advantageously, the switched-mode power supply circuit comprises a
transformer having a primary and at least one secondary, the primary
being connected to the first portion and the secondary being connected to
the second portion.

[0026] The transformer comprises a galvanic isolation element between its
input (primary of the transformer) and its output or outputs (secondaries
of the transformer).

[0027] Preferably, the detection means are capable of detecting a drop in
electrical current flowing in the primary of the transformer below a
predetermined current threshold as a function of the predetermined drop
in electrical consumption of the said component.

[0028] The current threshold is notably a function of the consumption at
rest of the component powered at low voltage.

[0029] Preferably, the detection means comprise a comparator. This
comparator compares the current flowing in the primary with the current
threshold. This comparison uses notably an image voltage of this current
flowing in the primary.

[0030] Advantageously, the electronic component is a microprocessor
controlling the power supply of a device via at least one component
amongst the second components.

[0031] According to a preferred embodiment, the device is a motor of a
compressor.

[0032] Advantageously, the predetermined drop corresponds to an idling of
the component.

[0033] Preferably, the board comprises means for inhibiting the switching
means when the board is switched on.

[0034] The invention also relates to a method for controlling a printed
circuit board, the said board comprising: [0035] a first portion having
first electronic components of which the earth electrode is on a first
voltage source; [0036] a second portion having second electronic
components of which the earth electrode is on a second voltage source;
[0037] a third portion inserted between the first portion and the second
portion and forming a potential barrier; [0038] a switched-mode power
supply circuit connecting the first portion and the second portion;

[0039] the said second portion also comprising at least one electronic
component powered by the said first voltage source via the switched-mode
power supply circuit,

[0040] the said method comprising the steps of: [0041] detection of a
drop in electrical consumption of the component; and [0042] switching of
the power supply when a predetermined drop in electrical consumption of
the said component is detected.

[0043] Advantageously, the predetermined drop corresponds to an idling of
the component and the method also comprises, before the switching step,
the steps of: [0044] reception by the component of an instruction to
switch the power supply; and [0045] idling of the component.

[0046] The invention also relates to a compressor housing comprising a
printed circuit board according to the invention.

[0047] Other features, details and advantages of the invention will emerge
more clearly on reading the description given below as an indication with
reference to the drawings in which:

[0048] FIG. 1 is a diagram illustrating the structure of a compressor for
a motor vehicle;

[0049]FIG. 2 is a diagram illustrating the detailed structure of a
printed circuit board of the compressor of FIG. 1, according to one
embodiment of the invention;

[0050]FIG. 3 is a diagram illustrating the structure of an example of a
switched-mode power supply circuit of the board according to one
embodiment of the invention;

[0051]FIG. 4 is a graphic illustrating the operation of a switched-mode
power supply circuit;

[0052]FIG. 5 is a diagram illustrating the structure of an example of
detection means of the board according to one embodiment of the
invention;

[0053]FIG. 6 is a flowchart illustrating the operating of the control
method according to the invention; and

[0054]FIG. 7 is a graphic illustrating an example of application of the
method according to the invention.

[0055] FIG. 1 illustrates a compressor 2 of an air conditioning device for
a motor vehicle in which the present invention can be applied. The
compressor 2 comprises a first housing 4 and a second housing 6.

[0056] The first housing 4 comprises a compression mechanism 8 with
electrical drive.

[0057] The first housing 4 also comprises an electric motor 10 for driving
the compression mechanism 8.

[0058] The second housing 6, usually made of aluminium, comprises a
printed circuit board 12 called a PCB for controlling the compression
mechanism 8. This PCB notably forms an inverter which powers and controls
the electric motor 10.

[0059] The PCB 12 is capable of being powered at low voltage and at high
voltage by a low-voltage power supply 14 and a high-voltage power supply
16 respectively.

[0060] A low voltage means a voltage lower than 60 V, typically equal to
12 V, and a high voltage means a voltage higher than 60 V, typically
equal to 305 V. The low voltage corresponds to the voltage available on a
protected network of the vehicle while the high voltage originates from
an electrical source that also powers an electric motor responsible for
driving the movement of the vehicle.

[0061]FIG. 2 illustrates the detailed structure of the board 12 according
to a preferred embodiment of the invention.

[0062] The board 12 comprises three distinct portions. The first portion
20 of the board 12 supports first electronic components 22 capable of
being powered at low voltage by the low-voltage power supply 14.

[0063] The second portion 24 of the board 12 supports second electronic
components 26 capable of being powered at high voltage by the
high-voltage power supply 16.

[0064] The third portion 28 is inserted between the first portion 20 and
the second portion 24. It forms a potential barrier between the two
portions 20, 24. This third portion 28 possesses no electrical tracks and
preferably has a minimum width of 4.5 mm.

[0065] The second portion 24 also comprises a microprocessor 30 powered at
low voltage by the power supply 14 via a switched-mode power supply
circuit 32.

[0066] In one variant, the microprocessor 30 is replaced by one or more
electronic components powered at low voltage by the power supply 14.

[0067] The microprocessor 30 is capable of controlling the power supply of
the motor 10 of the compressor 2 via a second component 26 powered at
high voltage, such as, for example, a power board connected to the motor
10 of the compressor 2.

[0068] The switched-mode power supply circuit 32 is placed so as to
straddle between the three portions 20, 28, 24 of the board 12. It is
connected as an input to the low-voltage power supply 14 and as an output
to the microprocessor 30.

[0069] The first portion 20 also comprises means 34 for detecting a drop
in electrical consumption of the microprocessor 30 in order to switch the
switched-mode power supply circuit 32 when a predetermined drop in
electrical consumption of the microprocessor 30 is detected.

[0070]FIG. 3 illustrates the structure of the switched-mode power supply
circuit 32 according to a preferred embodiment of the invention.

[0071] According to this preferred embodiment, the switched-mode power
supply circuit 32 is a Flyback converter. The Flyback converter comprises
a transformer 40 comprising a first inductor 42 and a second inductor 44
that are coupled together.

[0072] The first inductor 42, with a value L1 and having a number of turns
equal to N1, forms the primary of the transformer 40. It is connected to
the first portion 20 of the board 12.

[0073] The second inductor 44, with a value L2 and having a number of
turns equal to N2, forms the secondary of the transformer 40. It is
connected to the second portion 24 of the board 12.

[0075] The primary 42 is powered by the low-voltage power supply 14 via a
switch 48 comprising an MOSFET transistor, for example.

[0076] The secondary 44 is connected to a diode 50, itself connected to a
capacitor 52 connected in parallel to a load 54 comprising notably the
microprocessor 30.

[0077] The operation of the switched-mode power supply circuit 32 is
detailed with reference to the curves 60, 62, 64, 66 of FIG. 4 which
illustrate respectively the evolution of the primary current I42, of
the secondary current I44, of the primary voltage V42 and of
the load voltage V54 as a function of time.

[0078] The switched-mode power supply circuit 32 operates, over a
switching period T, according to a duty cycle equal to
α=tON/T, tON representing the period during which the
switch 48 conducts. The load voltage V54 is constant and equal to

V 0 = N 2 N 1 α 1 - α E DC
, ##EQU00001##

where EDC is the voltage delivered by the low-voltage power supply
14, α is the duty cycle of the power supply circuit, N1 is the
number of turns of the primary 42 and N2 is the number of turns of the
secondary 44.

[0079] In the on state, for the time t between 0 and tON, the switch
48 is closed. The primary 42 of the transformer 40 is directly connected
to the power supply 14 so that the voltage V42 of the primary is
equal to the voltage EDC generated by the power supply 14. The
result of this is an increase in the magnetic flux in the transformer 40.
The current I42 of the primary 42 then increases according to the
relation

I 42 = E DC L 1 t , ##EQU00002##

where t represents the time, EDC is the voltage delivered by the
low-voltage power supply 14 and L1 is the value of the inductor of the
primary 42.

[0080] At the end of the on state, I42 reaches its maximum value

I P = E DC L 1 t ON , ##EQU00003##

where tON represents the time during which the switch 48 conducts,
EDC is the voltage delivered by the low-voltage power supply 14 and
L1 is the value of the inductor of the primary 42.

[0081] Moreover, IP is a function of the power P of the components
connected to the secondary 44 according to the relation

I P = 2 * P L 1 * F d ##EQU00004##

where Fd is the switching frequency of the converter. It is
therefore possible to determine the time tON from the power P.

[0082] According to one embodiment not shown, the transformer comprises
two secondaries. The power P is obtained, according to this example, by
virtue of a secondary connected to the earth of the first portion coupled
with the secondary connected to the earth of the second portion and
powering the microprocessor.

[0083] Returning to FIG. 3, in the on state, the voltage at the terminals
of the secondary 44 is negative, thus blocking the diode 50 so that the
current of the secondary I44 is zero. It is the capacitor 52 that
supplies the energy demanded by the load 54.

[0084] At the end of the on state, at the time tON, the switch 48
opens thus preventing the current of the primary I42 from continuing
to flow. The conservation of the energy stored in the transformer 40
causes the appearance of a current I44 in the secondary of the
transformer 40 the initial value of which is equal to

I P × N 1 N 2 . ##EQU00005##

The current I44 is given by the relation

I 44 = I P × N 1 N 2 - V 0 L 2
( t - t ON ) I 44 ##EQU00006##

cancels out at t=t2.

[0085] The voltage of the primary V42, between tON and t2,
is given by the relation

V 42 = - N 1 N 2 V 0 . ##EQU00007##

It is zero between t2 and T.

[0086] Therefore, for a period, the switched-mode power supply circuit
operates in three distinct modes: a first mode M1 for the time between 0
and tON, a second mode M2 for the time between tON and t2
and a third mode M3 for the time between t2 and T.

[0087]FIG. 5 details the structure of the detection means 34 for
detecting a drop in consumption of the microprocessor 30. This drop in
consumption results in a drop in the electrical power at the secondary 44
involving a drop in the maximum current IP of the primary 42.

[0089] The comparator 70 comprises an error amplifier 71 receiving, on an
inverter input 72, a signal representing the maximum current IP of
the primary and, on a non-inverter input 74, a signal representing a
predetermined current threshold IS. This threshold is fixed by means
of a circuit 76 comprising two resistors R1 and R2 in series. The
threshold IS is chosen so as to correspond to a predetermined drop
in electrical consumption of the microprocessor 30. For example, the
predetermined drop in electrical consumption corresponds to an idling of
the microprocessor 30.

[0090] The detection means 34 also comprise means 78 for inhibiting the
comparator 70 during the start-up phase. These inhibition means 78
preferably comprise an RC circuit for raising the potential of the
non-inverter input 74 of the error amplifier 71 in order to always impose
a low state at the output 80 of the comparator 70 throughout the whole
start-up phase. Thus, there is no risk of switching the power supply 14
during the start-up phase.

[0091] The flowchart of FIG. 6 and the graphic of FIG. 7 detail the
operation of the method for controlling the power supply.

[0092] During a step 90, the compressor 2 is operating.

[0093] At step 92, the microprocessor 30 receives, for example from a CAN
bus of the vehicle, an instruction to stop the power supply of the
compressor 2. It then instructs the stopping of the compressor 2 and
enters, during the step 94, idling mode.

[0094] This causes a drop in the electrical consumption of the
microprocessor 30 which results in a drop in power at the secondary 44 of
the transformer and therefore a drop in the peak-to-peak current IP
of the primary 42.

[0095] At step 96, the detection means 34 compare the current IP with
the threshold IS. When the value of the current IP falls below
IS, the low-voltage power supply 14 is switched at step 98.

[0096] Naturally, other embodiments may be envisaged.

[0097] The board according to the invention has been described in an
example in which the switched-mode power supply is a Flyback converter.
However, the board according to the invention may comprise another type
of switched-mode power supply.